This invention relates to spring clutch mechanisms and to improved means for anchoring an end of the helical clutch spring. In one particular aspect the invention relates to the provision of an electromagnetically actuated spring clutch wherein the spring is permanently bound to the power input member.
Attachment between spring and power input or output member in spring clutch mechanisms has previously been accomplished by other methods. In one, a tab or tang extending either axially or radially from an end turn of the helical coil spring is inserted into a slot or cavity in the power transmitting member. In another, the several end turns of the spring are frictionally secured to the power transmitting drum, e.g. by reducing the diameter of the turns, or by increasing the number of contacting coils or the diameter of the drum. A further method involves the placing of a separate compressible split ring about the several end turns of the spring. These methods may be seen in the disclosures of U.S. Pat. Nos. 3,185,276; 3,373,851; 3,465,857; 3,735,847; 3,835,972; and 4,263,995.
The shaping of the spring wire to provide a partially constricted diameter or an additional tang involves added expense. An axial tang requires an axial cavity and limits desirable reduction in thickness of the member receiving the tang. A spring restrained by a tang is subject to "humping", a condition in which the adjacent coils do not return fully to their initial diameter and so cause an alteration of the "at rest" position of clutch-connected mechanism. The incorporation of a compressible split ring involves additional expense both in components and in assembly, and increases space requirements.